The therapeutic value of insulin and, in particular, human insulin in treating diabetic patients has long been appreciated. The primary commercial source of insulin for therapeutic application, however, has been that prepared from bovine or porcine pancreas. Because of such factors as the immunological differences between human and animal insulin which may result in the formation of anti-insulin antibodies after prolonged use in humans and the often uncertain availability of bovine and porcine pancreas, efforts to produce significant quantities of insulin from human pancreas have increased. To date, efforts to produce human insulin have concentrated on either the chemical synthesis or the biological cultivation of insulin-producing pancreatic cells. The chemical synthesis of human insulin involves several very complex steps and has proved to be quite costly on a large scale, particularly in comparison to the methods currently utilized for the commercial production of bovine and porcine insulin. The known biological methods for producing insulin are promising but are not without their limitations and disadvantages. Available and suggested methods are, for the most part, limited to insulin production under in vitro conditions. It would be highly desirable to provide a method of supplying a continuous, long term in vivo source of insulin to a diabetic patient. However, those methods which have potential in vivo as well as in vitro application have fallen short of expectations. In addition, some of the known in vitro biological methods are not suitable for the production of insulin on a large scale.
Current biological methods for producing human insulin have focused on cellular transformation, either of the growth rate, morphology and structure, of the cell function or some combination of these. For example, in U.S. Pat. No. 4,082,613, Thirumalachar et al. teach the extraction of the functional genomic material, that portion of the deoxyribonucleic acid (DNA) which controls the production of insulin, from human or other mammalian pancreatic beta epitheliod cells. This DNA fraction is then used to transform functionally a population of fungal cells to produce insulin. While the aforementioned process may be suitable for the in vitro production of insulin on a large scale, the application of the process is limited to in vitro conditions, and does not obviate the need for separately administering a therapeutic dose of insulin to the diabetic patient.
A method for producing insulin which has both in vitro and in vivo application was reported by Neisor et al. in Biochem. J., 178, 559-68 (1979), in which a primary culture of rat pancreatic endocrine cells was morphologically transformed by simian virus 40 (SV 40). The method reported therein, while promising, suffers nonetheless from some significant drawbacks regarding its application to humans, including the unconditional nature of the transformation, which makes control of the expression of the virus extremely difficult, and the potentially biohazardous effects associated with the SV 40 virus in humans.
The prior art has thus failed to disclose a method of producing an insulin-producing cell line comprising a primary culture of conditionally transformed insulin-producing pancreatic cells which may be utilized either in vitro as an exogenous insulin supply or in vivo in an individual patient to provide a long term endogenous source of insulin.